The present invention is directed to a method for monitoring the operation of optical fibers within a fully optical fiber-bound communication network, in which method at least two optical fibers are provided for the purpose of transmitting optical payload signals between a central optical equipment and an optical equipment at a decentralized location.
In fully optical fiber-bound communication networks of today, in particular in communication networks having a ring topology or a double-star topology, the communication equipment of a network customer, for instance an Internet provider, is connected to the fully optical communication network with the aid of a plurality of optical feed fibers or, respectively, pairs of fibers. Volumes of data in the gigabit range are typically transmitted via such optical feed fibers and the data is transmitted between the central equipment, for example a network node of a fully optical communication network, and a decentralized optical equipment, for instance a network terminal device. When data is transmitted at such high rates, the network customer demands from the network operator a high reliability of the fully optical communication network and of the connection to the fully optical communication network. In order to be able to ensure a perfect functioning of the connection of the communication equipment of the network customer to the fully optical communication network, this connection must be remotely monitored. This means that the information about the operational condition of the optical feed fibers for the respective network connection must be available in the respective network node. If, for example, a malfunction occurs for the connection of a network customer, without a remote monitoring of the connection of the network customer, it is impossible for the network operator to assess whether the malfunction is his own responsibility, for instance because a digging or excavating equipment has damaged one of the optical feed fibers, or if the error is the responsibility of the network customer, for instance because the transmitting laser is defective.
Therefore, it is advantageous to be able to automatically monitor, by means of a remote monitoring process, whether or not malfunctions or, respectively, interruptions in optical feed fibers are the responsibility of the network operator.
A method for xe2x80x9cmonitoring optical single-fiber connection lines up to a passive interfacexe2x80x9d is already known from German 43 28 486 A1, in which method, in order to be able to effectively monitor an optical B-ISDN subscriber terminal, a monitoring signal that is defined by the carrier impulses and is originally electronic is transmitted from an optical fiber cable (LWL) terminal unit, particularly the subscriber""s terminal unit at the network side, to a defined passive optical interface, whereby this monitoring signal is added in the fiber-optic terminal unit to the electrical control signal of the transmitter of this monitoring signal that is provided there. In addition, a small part of the optical signal that is transmitted from the fiber-optic terminal unit to the subscriber terminal (that is both the payload signal and the monitoring signal) is tapped at a passive optical interface and transmitted in the reverse direction to the fiber-optic terminal line, where it is converted into an electrical signal in the provided optical receiver potentially together with the optical signal being received from the subscriber.
In addition, the German Reference explicitly describes the evaluation of this type of back-fed electrical monitoring signal for the purpose of monitoring the subscriber terminal. But, this type of monitoring method is associated with an unfeasibly high technical outlay and, thus, unjustifiable costs. Furthermore, a high technical outlay is required in order to precisely separate the desired reflections at the passive interface from the additional reflections at other locations in order to be able to guarantee a high reliability of the monitoring method.
The object of the present invention is to simplify the monitoring of the operation of optical fibers in a fully optical fiber-bound communication network, particularly the monitoring of a plurality of feed fibers between a central equipment and a decentralized equipment, with respect to the technical outlay needed for the realization. This object is achieved by an improvement in a method for monitoring the operation of optical fibers in a fully optical fiber-bound communication network, wherein at least two optical fibers are provided for transmitting optical payload signals between the central and decentralized optical equipment with the improvements being that a central equipment generates an optical auxiliary signal and transmits this signal from the central optical equipment to the decentralized optical equipment via one of the optical fibers together with the first optical payload signal, the decentralized optical equipment receives this auxiliary optical signal, reroutes the signal and transmits the signal back to the central optical equipment in addition to the second optical payload signal via another optical fibers and that the central optical equipment monitors the reception of the retransmitted optical auxiliary signal.
The essential aspect of the invention is that the optical auxiliary signal that is generated in the central equipment is transmitted from the central optical equipment to the decentralized optical equipment together with a first optical payload signal via one of the optical fibers, and that the optical auxiliary signal that is received in the decentralized optical equipment is rerouted or redirected and transmitted back to the central optical equipment in addition to a second optical payload signal via another optical fiber. In addition, the reception of the retransmitted optical auxiliary signal in the central optical equipment is monitored optically. It is advantageous here that an additional optical auxiliary signal is generated in the network node and is transmitted to the network terminal device in addition to a payload signal via the complete feed fiber, whereby the auxiliary signal does not have to satisfy high quality requirements. Therefore, a cost-effective layer diode, or potentially an LED, respectively, can be used to generate this auxiliary signal. The auxiliary signal is coupled in and out of the central equipment or decentralized equipment, particularly, advantageously, using optical couplers so that an additional conversion of the optical auxiliary signal into an electrical signal is not necessary. The rerouting of the optical auxiliary signal in the decentralized equipment can also be realized by a simple additional optical fiber and, thus, does not require a high technical outlay. In other words, the network terminal device installed at the network customer comprises a simple passive structure and is, thus, extremely reliable. Furthermore, an external power source or supply for the network terminal device is not required locally at the network customer, which fact lends additional flexibility with respect to the selection of the location for operating the network terminal device. It is particulary advantageous that the normal operation of the optical fibers is indicated by the reception of the retransmitted optical auxiliary signal in the central optical equipment.
In addition to the optical auxiliary signal, the second optical payload signal is evaluated in the central optical equipment for the purpose of monitoring the operational condition of the two optical fibers. In this way, a fiber break or, respectively, a transmission failure in the optical fibers, via which the first optical payload signal is transmitted from the central to the decentralized equipment, can be detected particularly advantageously on the basis of an absence of a retransmitted optical auxiliary signal when this signal is not received and the second optical payload signal is received in the central optical equipment.
According to another development of the inventive method, at least a portion of the auxiliary signal received in the decentralized optical equipment is tapped, and the fiber condition information, which is contained in the tapped auxiliary signal, relating to the operational condition of at least one optical fiber is indicated in the decentralized optical equipment. In addition, the frequency of the optical auxiliary signal lies in the optically visible frequency range and comprises an optical power intensity of less than two milliwatts in the generation process in the network node. This is associated with the advantage that a portion of the optical signal can be tapped in the network terminal device and indicated to the network customer at the network terminal device directly, without endangering the eyesight of the maintenance personnel. Thus, the network customer receives information about the operational condition of the feed fibers from the network node to the network terminal device in a particularly simple and efficient manner and, when a failure of the feed fiber is occurring, this customer can report this information to the network operator by telephone.